This investigation is directed towards defining the developmental aspects of bile acid metabolism in the preterm infant. Studies include an evaluation of the metabolism, conjugation, sulfation and secretion of lithocholic acid will be performed in the fetal sheep using an established animal model. Bile acid kinetics in the human infant are performed utilizing a non-radioactive stable isotope dilution technique with 13C and deuterium labeled bile acids. The influence of dietary lipid on bile acid kinetics will be determined and the mechanisms for bile acid conjugation and secretion will be investigated. The interaction between bile acid synthesis and cholesterol excretion will be determined in children with homozygous hyperlipoproteinemia type II utilizing this methodology. In addition, other descriptions of gastrointestinal function and specific malabsorption syndromes will be evaluated utilizing a recently devised non-radioactive 13CO2 breath test. BIBLIOGRAPHIC REFERENCES: Franklin, F.A., Watkins, J.B., Heafitz, L., Clowes, A.W. and Breslow, J.L.: Serum lipids during total parenteral nutrition with Intralipid (TPN-IL). Pediatric Research, 10:354, 1976. (abst). Watkins, J.B. and Perman, J.A.: Bile acid metabolism in infants and children. Clinics in Gastroenterology. In press. January, 1977.